The present invention relates to a clutch for vehicles having a first supply cylinder which is actuated by a clutch pedal and which is connected via a fluid line to a second receiving cylinder. The clutch further has a safety device connected within the fluid line between the first and the second cylinder, the safety device having at least one throttle element for reducing the fluid flow from the second to the first cylinder when a preset engaging speed for engaging the clutch is surpassed. The safety device also has a measuring orifice that is connected in parallel to the throttle element, wherein a closing means is provided for closing the fluid line between the first and the second cylinders with the exception of the throttle element when a preset fluid pressure differential, measured before and behind the measuring orifice, is surpassed.
Such clutches are hydraulically disengaged via the first supply cylinder and the receiving cylinder connected thereto by pressing down the clutch pedal. When driving off from a stop, the clutch must transfer the required engine torque for a rpm difference between the crankshaft and the gear shaft. This takes place during the engagement of the clutch and requires a sensitive handling on the part of the driver for the actuation (engaging) speed of the clutch depending on the gear in use as well as on the accelerator position from which the engine torque results.
Sometimes it happens that the foot of the driver accidentally slips off the clutch pedal so that the clutch pedal is suddenly released. Then the clutch engages with the highest possible engaging speed. This may result in damage to parts of the drive train and the tires since the resulting torque peak values may be a multiple of the nominal torque value of the engine.
In the known clutch of German Offenlegungschrift 37 36 584 the fluid connection between the supply and the receiving cylinder comprises a safety device in the form of a closing body. The closing body has axial grooves at its circumference via which the fluid can flow upon actuation of the clutch pedal. Furthermore, the closing body is penetrated by an axial bore which forms a throttle element. When undesirably high engaging speeds occur, the fluid will be dammed or restricted at the end face of the closing body and forces the closing body against the force of a spring into it closed position in which its end face rests at the housing wall. In this closed position, the axial grooves are closed so that the fluid on its return from the second cylinder to the first cylinder can only pass through the throttle element. This results in a reduction of the flow velocity, and the engaging speed of the clutch is reduced. The closing body is maintained in its open position by a coiled pressure spring. This coiled pressure spring has an increasing force-travel distance characteristic curve. This causes the closing body to be moved towards its closing position upon occurrence of the pressure head not suddenly, but slowly in correspondence to the characteristic curve of the spring. Therefore, only a slow throttle of the fluid flow occurs.
In another clutch known from German Gebrauchsmuster 17 85 882 the fluid flowing from the first supply to the second receiving cylinder and vice versa is throttled during engagement and disengagement of the clutch. When the hydraulic medium returns from the second cylinder to the first cylinder, a throttle disk is first comes to rest at the cylinder bottom so that the hydraulic medium can only flow through the throttle element of the throttle disk into the line toward the first cylinder. This throttling effect occurs every time when the clutch pedal is released.
It is an object of the present invention to provide a clutch of the aforementioned kind with which during a sudden release of the clutch pedal the main fluid path for the fluid from the second cylinder to the first cylinder is immediately closed.